Passivated and Faceted for Fin Field Effect Transistor

ABSTRACT

A fin field effect transistor (FinFET), and a method of forming, is provided. The FinFET has a fin having one or more semiconductor layers epitaxially grown on a substrate. A first passivation layer is formed over the fins, and isolation regions are formed between the fins. An upper portion of the fins are reshaped and a second passivation layer is formed over the reshaped portion. Thereafter, a gate structure may be formed over the fins and source/drain regions may be formed.

This application is a continuation of U.S. patent application Ser. No.16/538,496, entitled “Passivated and Faceted for Fin Field EffectTransistor” filed on Aug. 12, 2019, which is a continuation of U.S.patent application Ser. No. 15/620,499, now U.S. Pat. No. 10,381,482issued Aug. 13, 2019, entitled “Passivated and Faceted for Fin FieldEffect Transistor” filed on Jun. 12, 2017, which is a continuation ofU.S. patent application Ser. No. 15/018,245, now U.S. Pat. No. 9,680,021issued Jun. 13, 2017, entitled “Passivated and Faceted for Fin FieldEffect Transistor” filed on Feb. 8, 2016, which is a divisional of U.S.patent application Ser. No. 14/051,033, now U.S. Pat. No. 9,287,262issued Mar. 15, 2016, entitled “Passivated and Faceted for Fin FieldEffect Transistor” filed on Oct. 10, 2013, which applications are herebyincorporated herein by reference.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a finfield effect transistor (FinFET). A typical FinFET is fabricated with athin vertical “fin” (or fin structure) extending from a substrate formedby, for example, etching away a portion of a silicon layer of thesubstrate. The channel of the FinFET is formed in this vertical fin. Agate is provided over (e.g., wrapping) the fin. Having a gate on bothsides of the channel allows gate control of the channel from both sides.In addition, strained materials in source/drain (S/D) portions of theFinFET utilizing selectively grown silicon germanium (SiGe) may be usedto enhance carrier mobility.

However, there are challenges to implementation of such features andprocesses in complementary metal-oxide-semiconductor (CMOS) fabrication.For example, interface traps between fins and shallow-trench-isolation(STI) oxide cause high leakage current of the FinFET, thereby degradingthe device performance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a flowchart illustrating a method of fabricating a FinFETaccording to various aspects of the present disclosure;

FIG. 2 shows a top view of a FinFET comprising a passivation structureaccording to various aspects of the present disclosure;

FIGS. 3-10 are cross-sectional views of a FinFET at various stages offabrication according to various embodiments of the present disclosure;

FIGS. 11-18 are cross-sectional views of a FinFET at various stages offabrication according to various other embodiments of the presentdisclosure; and

FIGS. 19-26 are cross-sectional views of a FinFET at various stages offabrication according to various other embodiments of the presentdisclosure.

DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of thedisclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed between the firstand second features, such that the first and second features may not bein direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

Referring to FIG. 1, illustrated is a flowchart of a method 100 offabricating a fin field effect transistor (FinFET) according to variousaspects of the present disclosure. The method 100 begins with step 102in which a substrate, such as a silicon substrate, is provided. Themethod 100 continues with step 104 in which one or more semiconductorlayers are formed over the substrate. In an embodiment, such as thatdisclosed below with reference to FIGS. 3-10, the one or moresemiconductor layers comprise a silicon germanium epitaxially grown overthe substrate and a germanium layer epitaxially grown over the silicongermanium layer. In another embodiment, such as that disclosed belowwith reference to FIGS. 11-18, a silicon germanium layer (gradient oruniform) is formed over the substrate. In yet another embodiment, suchas that disclosed below with reference to FIGS. 19-26, the one or moresemiconductor layers comprise a plurality of silicon germanium layershaving differing concentrations of germanium.

In step 106, a plurality of trenches is formed through the one or moresemiconductor layers and into the substrate, wherein fins are createdbetween adjacent trenches. A first passivation layer, such as anoxynitride layer, is formed over the fins in step 108, followed byisolation regions being formed by depositing a dielectric material inthe trenches in step 110. Exposed portions of the fins are reshaped anda second passivation layer, such as an oxynitride layer, is formed overthe reshaped fins in step 112. Thereafter, a gate structure is formed instep 114. The discussion that follows illustrates embodiments of FinFETsthat can be fabricated according to the method 100 of FIG. 1.

FIG. 2 shows a top view of a fin field effect transistor (FinFET) 200comprising a passivation structure 230 formed over a fin structure 220according to various aspects of the present disclosure. FIGS. 3-26 arecross-sectional views of a FinFET 200 taken along the line a-a of FIG. 2at various stages of fabrication according to various embodiment of thepresent disclosure. As employed in the present disclosure, the FinFET200 refers to any fin-based, multi-gate transistor. Other transistorstructures and analogous structures are within the contemplated scope ofthe disclosure. The FinFET 200 may be included in a microprocessor,memory cell, and/or other integrated circuit (IC).

It is noted that the method of FIG. 1 does not produce a completedFinFET 200. A completed FinFET 200 may be fabricated using complementarymetal-oxide-semiconductor (CMOS) technology processing. Accordingly, itis understood that additional processes may be provided before, during,and after the method 100 of FIG. 1, and that other processes may only bebriefly described herein. Also, FIGS. 1-26 are simplified for a betterunderstanding of the concepts of the present disclosure. For example,although the figures illustrate the FinFET 200, it is understood the ICmay comprise a number of other devices comprising resistors, capacitors,inductors, fuses, etc.

FIG. 2 illustrates a FinFET 200 fabricated using the steps in FIG. 1.For illustration, the FinFET 200 comprises a fin structure 220 (dashedline), a passivation structure 230 surrounding the fin structure 220 anda gate structure 240 traversing over a channel portion of the finstructure 220. For illustration, the FinFET 200 comprises two fins. Insome embodiments, the FinFET 200 may comprise less than or greater thantwo fins, for example, one fin or three fins.

FIGS. 3-10 illustrate various cross-sectional views of intermediatesteps of fabricating a FinFET device in accordance with an embodiment.Referring first to FIG. 3 and step 102 in FIG. 1, a substrate 202 isprovided, wherein the substrate 202 comprises a first semiconductormaterial having a first lattice constant and hence is also referred toas first semiconductor material 202 in the present disclosure. In oneembodiment, the substrate 202 comprises a crystalline silicon substrate(e.g., wafer). In alternative embodiments, the substrate 202 comprises asilicon-on-insulator (SOI) structure. The substrate 202 may comprisevarious doped regions depending on design requirements (e.g., p-typesubstrate or n-type substrate). In some embodiments, the doped regionsmay be doped with p-type or n-type dopants. For example, the dopedregions may be doped with p-type dopants, such as boron or BF₂; n-typedopants, such as phosphorus or arsenic; and/or combinations thereof. Thedoped regions may be configured for an n-type FinFET, or alternativelyconfigured for a p-type FinFET.

Still referring to FIG. 3, a second semiconductor material 204 (such assilicon germanium layer 204) epitaxially grown over the siliconsubstrate 202 (step 104 in FIG. 1), wherein the second semiconductormaterial 204 has a second lattice constant greater than the firstlattice constant. For example, in an embodiment, the substrate 202 maybe a silicon wafer and the second semiconductor material 204 is asilicon germanium layer. In this example, the germanium layer has about25% to about 75% germanium, and may have a strained or fully relaxedsurface. Additionally, the second semiconductor material 204 may be auniform layer having a uniform concentration of, for example, germanium,or a gradient layer wherein the concentration of, for example, germaniumvaries.

In an embodiment, the second semiconductor material 204 (such as silicongermanium layer) is selectively grown by a chemical vapor deposition(CVD) process, such as a low-pressure CVD (LPCVD). In one embodiment,the LPCVD process is performed at a temperature of about 350° C. toabout 800° C. and under a pressure of about 1 mTorr to about 760 Torr,using, for example, SiH₄, Si₂H₆, or the like as a silicon precursor andGeH₄, Ge₂H₆, or the like as a germanium precursor. In some embodiments,the silicon germanium layer 204 has a thickness ranging from about 10 nmto about 50 nm.

Still referring to FIG. 3, a third semiconductor material 206 (such as agermanium layer) is epitaxially grown over the second semiconductormaterial 204 (step 104 in FIG. 1), wherein the third semiconductormaterial 206 has a third lattice constant greater than the secondlattice constant. As such, the second lattice constant is between thefirst lattice constant and the third lattice constant. In an embodiment,the third semiconductor material 206 comprises a germanium layerselectively grown by an LPCVD process. In an embodiment, the LPCVDprocess is performed at a temperature of about 200° C. to about 700° C.and under a pressure of about 1 mTorr to about 760 Torr, using GeH₄ orGe₂H₆ as a precursor. In some embodiments, the third semiconductormaterial 206 has a thickness ranging from about 10 nm to about 50 nm. Inan embodiment, a surface of the third semiconductor material 206 isfully relaxed.

For convenience, the second semiconductor material 204 is also referredto herein as the silicon germanium layer 204, and the thirdsemiconductor material 206 is also referred to herein as the germaniumlayer 206. It should be noted, however, that other embodiments mayutilize other materials, such as other group III-V materials, SiC, andthe like.

FIGS. 4-5 illustrate forming a plurality of trenches (such as trenches210 in FIG. 5) into the substrate 202, the silicon germanium layer 204,and the germanium layer 206 in accordance with an embodiment, similar tothat discussed above with reference to step 106 in FIG. 1. Referringfirst to FIG. 4, there is shown a patterned mask 208 defining openings208 a. In an embodiment, the patterned mask 208 is a photoresist layerthat has been deposited, exposed, and developed. Other masking layers,such as oxide and/or nitride hard mask layers, may also be used.

The exposed germanium layer 206 is then etched to form a plurality oftrenches 210. In some embodiments, the plurality of trenches 210 extendsthrough the germanium layer 206, silicon germanium layer 204, and intothe silicon substrate 202. In some embodiments, the trenches 210 may bestrips (viewed from the top of the FinFET 200) parallel to each other,and closely spaced with respect to each other. In some embodiments, thetrenches 210 may be continuous and surrounding the remaining germaniumlayer 206 and remaining silicon germanium layer 204. In someembodiments, the etching process may be performed using CF₄, HBr, CH₃F,SF₆, a mixture thereof, or the like as an etching gas, a carrier gassuch as He or the like, and an passivation gas such as O₂ or the like.In an embodiment the process gas may be a combination of the etchinggas, a carrier gas, and a passivation gas and may be used to etch theGe, SiGe, and the Si material, although at different etch rates. In anembodiment, the trenches 210 may have a depth D1 of about 20 nm to about120 nm.

In the depicted embodiments, the remaining germanium layer 206,remaining silicon germanium layer 204, and remaining silicon substrate202 between trenches 210 are form a fin structure 220 (shown in FIG. 5).Further, the remaining germanium layer 206 is hereinafter referred to asan upper fin portion 220 u. The remaining silicon germanium layer 204 ishereinafter referred to as a middle fin portion 220 m. The protrudingsections of the substrate 202 between trenches 210 are hereinafterreferred to as a lower fin portion 2201.

As such, the fin structure 220 comprises a lower fin portion 2201comprising a first semiconductor material 202 having a first latticeconstant; a middle fin portion 220 m comprising a second semiconductormaterial 204 having a second lattice constant greater than the firstlattice constant; and an upper fin portion 220 u comprising a thirdsemiconductor material 206 having a third lattice constant greater thanthe first lattice constant and the second lattice constant, wherein themiddle fin portion 220 m is between the lower fin portion 2201 and upperfin portion 220 u. In the depicted embodiment, there are three finsextending from the substrate 202.

The patterned mask 208 is removed and a cleaning process is performed.In an embodiment, an SPM clean comprising a dilute mixture of H₂SO₄ andH₂O₂ may be used. Additionally, a cleaning process using, for example,diluted hydrofluoric (DHF) acid may be performed to remove a nativeoxide of the silicon substrate 202.

The process steps up to this point have provided the substrate 202having the trenches 210 surrounding the fin structure 220.Conventionally, by introducing a dielectric material, such asshallow-trench-isolation (STI) oxide, in the trenches 210, each fin ofthe fin structure 220 is isolated from neighboring fins. However, thestep of forming the dielectric material may create interface trapsbetween the fin and dielectric material. The generated interface trapsmay provide a carrier transportation path between the fin and thedielectric material and cause high leakage current of the FinFET,thereby degrading the device performance.

Accordingly, the processing discussed below forms a passivationstructure on exposed surfaces of the fin structure 220 to impedegeneration of the interface traps between the fin and STI oxide.Problems associated with high leakage current due to high interfacetraps may be reduced and/or avoided. Thus, embodiments disclosed hereinmay achieve the desired device performance characteristics, such as lowleakage.

As depicted in FIG. 6, and discussed above with reference to step 108 inFIG. 1, a passivation structure is formed on exposed surfaces of the finstructure 220 to enhance device performance. In an embodiment, thepassivation structure 230 is an oxynitride formed by an oxidation andnitridation process. As discussed above, the fin structure 220 may beformed of different materials, such as the silicon substrate 202, thesilicon germanium layer 204 and the germanium layer 206. The oxidationand nitridation processes may react differently with these materials,forming, for example, a silicon oxynitride (SiON) layer on the siliconsubstrate 202, a silicon germanium oxynitride (SiGeON) on the silicongermanium layer 204, and a germanium oxynitride (GeON) on the germaniumlayer 206. The first passivation layer may have a thickness of about 0.5nm to about 5 nm.

Accordingly, FIG. 6 illustrates a first passivation layer 230 comprisinga lower passivation portion 2301 over the silicon substrate 202, amiddle passivation portion 230 m over the silicon germanium layer 204,and an upper passivation portion 230 u over the germanium layer 206. Dueto the different materials, the lower passivation portion 2301 over thesilicon substrate 202 is a SiON layer, the middle passivation portion230 m over the silicon germanium layer 204 is a SiGeON layer, and theupper passivation portion 230 u over the germanium layer 206 is a GeONlayer.

As such, the first passivation layer 230 over the fin structure 220comprises the lower passivation portion 2301 over the lower fin portion2201 comprising an oxynitride of the first semiconductor material 202;the upper passivation portion 230 u over the upper fin portion 220 ucomprises an oxynitride of the third semiconductor material 206; and themiddle passivation portion 230 m between the lower passivation portion2301 and upper passivation portion 230 u, wherein the middle passivationportion 230 m over the middle fin portion 220 m comprises an oxynitrideof the second semiconductor material 204.

The first passivation layer 230 acts as a buffer layer between the fin220 and a subsequently formed insulating layer (such as STI oxide 216 inFIG. 8) to impede generation of the interface traps. Problems associatedwith high leakage current due to high interface traps may be reducedand/or avoided, thereby achieving better performance characteristics,such as low leakage.

In the depicted embodiment, the step of forming the first passivationlayer 230 over the fin structure 220 is performed by an oxidationprocess, followed by a nitridation process. In some embodiments, theoxidation process comprises a rapid thermal oxidation (RTO) process,high pressure oxidation (HPO), chemical oxidation process, in-situstream generation (ISSG) process, or enhanced in-situ stream generation(EISSG) process. In some embodiments, the RTO process is performed at atemperature of about 400° C. to about 700° C., using O₂ and O₃ asreaction gases, for about 1 second to about 30 seconds. In otherembodiments, an HPO is performed using a process gas of O₂, O₂+N₂, N₂,or the like at a pressure from about 1 atm to about 25 atm and atemperature from about 300° C. to about 700° C. for about 1 minute toabout 180 minutes. Examples of a chemical oxidation process include wetSPM clean, wet O₃/H₂O, or the like. The O₃ may have a concentration ofabout 1 ppm to about 50 ppm.

In some embodiments, the nitridation process comprises rapid thermalnitridation (RTN) process, high pressure nitridation (HPN), or decoupledplasma nitridation (DPN) process. In some embodiments, the RTN processis performed at a temperature of about 400° C. to about 800° C., usingNH₃ as reaction gas, for about 1 second to about 180 seconds. In someembodiments, the HPN process is performed using a process gas of NH₃ ata pressure from about 1 atm to about 25 atm and a temperature from about300° C. to about 700° C. for about 1 minute to about 180 minutes. Insome embodiments, the DPN process is performed under a power of about300 Watts to about 2250 Watts, using a process gas of N₂, NH₃, N₂+Ar,N₂+He, NH₃+Ar, or the like as process gases.

In some embodiments, a post nitridation anneal (PNA) process isperformed after the DPN process. In some embodiments, the PNA isperformed at a temperature of about 400° C. to about 700° C., using N₂as anneal gas, for about 1 second to about 180 seconds. The PNA processcauses the GeO to react with the N to reach a stable state, as well asdriving the N deeper to create a more uniform layer.

The ratio of y:x (N:O) in the oxynitride layers (e.g., SiO_(x)N_(y),SiGeO_(x)N_(y), and GeO_(x)N_(y)) may be controlled through processcondition adjustment, such as plasma power or temperature, for aparticular application. In some embodiments, a ratio of y:x is betweenabout 0.25 to about 0.90.

In some embodiments, some elements in the second semiconductor material204 (such as germanium in the silicon germanium layer 204) may diffuseinto the first semiconductor material 202 (such as the silicon substrate202) during the nitridation process. As such, the middle passivationportion 230 m may extend along a portion over the lower fin portion2201. In some embodiments, a first height H₁ of the middle passivationportion 230 m is equal to or greater than a second height H₂ of themiddle fin portion 220 m as illustrated in FIG. 6. In some embodiments,a ratio of the first height H₁ to the second height H₂ is from about 1to about 1.2.

FIG. 7 depicts the resulting structure after forming a dielectricmaterial 212 in the trenches 210, such as discussed above with referenceto step 110 of FIG. 1. The dielectric material 212 may include siliconoxide, and hence is also referred to as STI oxide 212 in the presentdisclosure. In some embodiments, other dielectric materials, such assilicon nitride, silicon oxynitride, fluoride-doped silicate glass(FSG), or a low-K dielectric material, may also be used. In someembodiments, the STI oxide 212 may be formed using a spin-on-dielectric(SOD) process, such as hydrogen silsesquioxane (HSQ) or methylsilsesquioxane (MSQ). In other embodiments, the STI oxide 212 may beformed using a high-density-plasma (HDP) CVD process, using silane(SiH₄) and oxygen (O₂) as reacting precursors. In other embodiments, theSTI oxide 212 may be formed using a sub-atmospheric CVD (SACVD) processor high aspect-ratio process (HARP), wherein process gases may comprisetetraethylorthosilicate (TEOS) and ozone (O₃).

In an embodiment, the STI oxide 212 is formed to a thickness greaterthan a height of the fins 220 and subsequently recessed using aplanarization process and an etch process. The planarization process,such as a CMP, reduces the STI oxide 212 to an upper surface of thefirst passivation layer 230. A subsequent etch process reduces theheight of the STI oxide 212 to expose portions of the sidewalls of thefin 220, resulting in recesses 214.

In some embodiments, the etching step may be performed using a wetetching process, for example, by dipping the substrate 202 in dilutehydrofluoric acid (HF). In some embodiments, the etching step may beperformed using a vapor etching process, for example, the vapor etchingprocess may be performed using HF as etching gas.

In an embodiment, the STI oxide 212 is recessed such that an uppersurface of the STI oxide 212 is at or below an interface between theupper fin portion 220 u and the middle fin portion 220 m. In anembodiment, a height H₃ of the exposed fin is about 10 nm to about 50nm, and width W₃ is about 6 nm to about 20 nm.

Referring now to FIG. 8, a fin reshaping process is performed inaccordance with an embodiment, and as discussed above with reference tostep 112 of FIG. 1. The reshaping process results in multiple crystalfacets being exposed along a surface of the fin 220. For example, in anembodiment an upper surface of the fin 220 may have a crystalorientation of (001) and a sidewall of the fin 220 may have a crystalorientation of (110). Between these crystal orientations, the finsurface may also exhibit crystal orientations of (113) and (111). Byreshaping the fin, higher mobility may be obtained as compared tounshaped fins. In an embodiment in which the upper fin portion 220 ucomprises germanium, the reshaping may be performed using a wet etch ofhot ammonia at a temperature of 20° C. to about 100° C. Such an etchprocess removes the upper passivation portion 230 u and reshapes theupper fin portion 220 u. As a result of the reshaping process, exposedportions of the fin 220 exhibits slanted sidewalls.

FIG. 9 illustrates a second passivation process in accordance with anembodiment, and as discussed above with reference to step 112 of FIG. 1.The second passivation process results in a second passivation layer 910formed on exposed surfaces of the reshaped fin, the upper fin portion220 u in the illustrated embodiment. The second passivation process mayuse similar processes as the first passivation process discussed abovewith reference to FIG. 6. The second passivation layer 910 may have athickness of about 0.5 nm to about 5 nm.

In some embodiments, the second passivation layer 910 comprisesGeO_(x)N_(y), wherein the ratio of y:x (N:O) is about 0.25 to about 0.9.A ratio such as this has been found to allow for a Dit (interface trapdensity—a measure of dangling bond concentration per cm²) of about1E10/cm2, whereas without the second passivation layer the Dit may beless than 1E12, such as about 1E11.

Furthermore, the y:x ratio of the second passivation layer along a topsurface of the upper fin portion 220 u may be adjusted to be differentfrom the y:x ratio of the second passivation layer along sidewalls ofthe upper fin portion 220 u. The y:x ratio of the second passivationlayer oxynitride may be controlled through process condition adjustment,such as plasma power or temperature. In some embodiments, a first ratioof y:x of the second passivation layer 910 along an upper surface of theupper fin portion 220 u is equal to or greater than a second ratio ofy:x of the second passivation layer 910 along sidewalls of the upper finportion 220 u. In some embodiments, a ratio of the first ratio to thesecond ratio is from about 1 to about 1.3. In some embodiments, a highery:x ratio may result in a lower etching rate or lower thermal effect.

Thereafter, additional processes may be performed. For example, FIG. 10illustrates a gate structure 912 formed over portions of the fin 220.Portions of the upper fin portion 220 u comprise source/drain (S/D)regions along either side of the gate electrode 912 b, and a channelregion extends between the S/D regions below the gate electrode 912. Insome embodiments, the gate structure 912 comprises a gate dielectric 912a and a gate electrode 912 b as shown in FIG. 10.

As illustrated in FIG. 10 the first passivation layer and/or the secondpassivation layer over the fin structure 220 to impede generation of theinterface traps between the fin 220 and STI oxide 212, or anotheroverlying dielectric (e.g., an interlayer dielectric), problemsassociated with high leakage current due to high interface traps may bereduced and/or avoided, thereby resulting in increased deviceperformance characteristics, such as low leakage.

It is understood that the FinFET 200 may undergo further processes. Forexample, CMOS processes may be performed to form various features suchas contacts/vias, interconnect metal layers, dielectric layers,passivation layers, etc.

FIGS. 11-18 illustrate various intermediate process steps of anotherembodiment. As discussed above, FIGS. 3-10 illustrate an embodiment inwhich the fins 220 comprise a lower fin portion 2201, a middle finportion 220 m, and a upper fin portion 220 u, wherein each has adifferent composition. As explained below FIGS. 11-18 illustrate anembodiment in which the fins will be formed of two different materials,rather than the three different materials as illustrated in FIGS. 3-10.Where appropriate, reference is made to the structures and processesdescribed above, wherein like reference numerals refer to like elementsunless otherwise noted.

Referring first to FIG. 11, there is shown the substrate 202 having thesecond semiconductor material 204 (also referred to as the silicongermanium layer 204) formed thereon. As discussed above the substrate202 may be formed of silicon and the second semiconductor material 204may be formed of silicon germanium, wherein similar processes asdescribed above with reference to FIG. 3 may be used.

In this embodiment, the silicon germanium layer 204 may be epitaxiallygrown to a thickness of about 20 nm to about 50 nm. The silicongermanium layer 204 may exhibit a strained surface and have aconcentration of germanium from about 25% to about 75%.

FIGS. 12 and 13 illustrate the patterning of the substrate 202 and thesilicon germanium layer 204, thereby forming trenches 210 interposedbetween fins 220. In this embodiment as illustrated in FIG. 13, the fins220 comprise a lower fin portion 2201 and a upper fin portion 220 u. Inan embodiment, the lower fin portion 2201 is formed from a siliconsubstrate and may be patterned in a similar manner as the lower finportion 2201 discussed above with reference to FIGS. 4 and 5, and theupper fin portion 220 u is formed from a silicon germanium material andmay be patterned in a similar manner as the middle fin portion 220 m(formed also of silicon germanium) discussed above with reference toFIGS. 4 and 5. It is noted that for convenience, that FIGS. 13-18 referto a upper fin portion 220 u, although the material of the upper finportion 220 u may be different than the material of the upper finportion 220 u referred to in FIGS. 5-10. It is also noted that othermaterials may be used. In an embodiment a depth Di of the trench isabout 20 nm to about 120 nm.

FIG. 14 illustrates a first passivation process to form a firstpassivation layer 230 in accordance with an embodiment. Similarprocesses as those disclosed above with reference to FIG. 6 may be used.In an embodiment, the first passivation layer 230 comprises anoxynitride. For example, in an embodiment in which the lower fin portion2201 comprises a silicon substrate, a lower passivation portion 2301 maybe formed of silicon oxynitride and in an embodiment in which the upperfin portion 220 u comprises silicon germanium, an upper passivationportion 230 u may be formed of silicon germanium oxynitride.

FIG. 15 illustrates forming an STI oxide 212 in the trenches 210 (seeFIG. 14), creating recesses 214, in accordance with an embodiment.Similar processes as those disclosed above with reference to FIG. 7 maybe used. In an embodiment, a height H₃ of the fin 220 above an uppersurface of the STI oxide 212 is about 10 nm to about 50 nm, and a widthW₃ of 6 nm to about 20 nm.

FIG. 16 illustrates a fin reshaping process and FIG. 17 illustrates asecond passivation process to form a second passivation layer 910 inaccordance with an embodiment. Similar processes as those disclosedabove with reference to FIGS. 8 and 9 may be used.

Thereafter, additional processes may be performed. For example, FIG. 18illustrates a gate structure 912 formed over portions of the fin 220.Similar processes and structures may be used as discussed above withreference to FIG. 10.

FIGS. 19-26 illustrate various intermediate process steps of anotherembodiment. As discussed above, FIGS. 3-10 illustrate an embodiment inwhich the fins 220 comprise a lower fin portion 2201, a middle finportion 220 m, and an upper fin portion 220 u, wherein each has adifferent composition, and FIGS. 11-18 illustrate an embodiment in whichthe fins 220 comprise a lower fin power 2201 and a upper fin portion 220u. As explained below FIGS. 19-26 illustrate an embodiment in which thefins will be formed of two different materials wherein the elementalconcentrations of one element varies, rather than the three differentmaterials as illustrated in FIGS. 3-10 and two different materials asillustrated in FIGS. 11-18. Where appropriate, reference is made to thestructures and processes described above, wherein like referencenumerals refer to like elements unless otherwise noted.

Referring first to FIG. 19, there is shown the substrate 202 having thesecond semiconductor material 204 (also referred to as the silicongermanium layer 204) formed thereon. As discussed above the substrate202 may be formed of silicon and the second semiconductor material 204may be formed of silicon germanium, wherein similar processes asdescribed above with reference to FIG. 3 may be used.

In this embodiment, the silicon germanium layer 204 comprises a firstsilicon germanium layer (Si_(x1)Ge_(y1)) 204 a and a second silicongermanium layer (Si_(x2)Ge_(y2)) 204 b, wherein the relativeconcentrations of germanium differs between the first silicon germaniumlayer 204 a and the second silicon germanium layer 204 b. The firstsilicon germanium layer 204 a may act as a buffer layer to the secondgermanium layer 204 b to reduce defects and to control the strain in asurface of the second germanium layer 204 b. In an embodiment, y1 isless than y2, thereby creating a compressive strain in a surface of thesecond germanium layer 204 b. In an embodiment, y2 is less than y1,thereby creating a tensile strain in a surface of the second germaniumlayer 204 b.

In an embodiment, the first silicon germanium layer 204 a may beepitaxially grown to a thickness of about 20 nm to about 50 nm and thesecond silicon germanium layer 204 b may be epitaxially grown to athickness of about 20 nm to about 50 nm.

FIGS. 20 and 21 illustrate the patterning of the substrate 202, thefirst silicon germanium layer 204 a and the second silicon germaniumlayer 204 b, thereby forming trenches 210 interposed between fins 220.In the illustrated embodiment, the fins 220 comprises a lower finportion 2201, a middle fin portion 220 m, and a upper fin portion 220 u,formed from the substrate 202, the first silicon germanium layer 204 aand the second silicon germanium layer 204 b, respectively. It is notedthat for convenience, that FIGS. 21-26 refer to a middle fin portion 220m and a upper fin portion 220 u, although the material of the middle finportion 220 m and the upper fin portion 220 u of FIGS. 21-26 may bedifferent than the material of the middle fin portion 220 m and theupper fin portion 220 u referred to in FIGS. 5-10. In an embodiment inwhich the substrate 202 is a silicon substrate, the substrate 202 may beetched as discussed above with reference to FIGS. 4 and 5. In anembodiment in which the first silicon germanium layer 204 a and thesecond silicon germanium layer 204 b are formed of silicon germanium,the first silicon germanium layer 204 a and the second silicon germaniumlayer 204 b may be etched in a similar manner as the silicon germaniumlayer discussed above with reference to FIGS. 4 and 5. In an embodimenta depth D1 of the trench is about 20 nm to about 120 nm.

FIG. 22 illustrates a first passivation process to form a firstpassivation layer 230 in accordance with an embodiment. Similarprocesses as those disclosed above with reference to FIG. 6 may be used.In this embodiment, the first passivation process results in a lowerpassivation portion 2301, a middle passivation portion 230 m, and anupper passivation portion 220 u, although the middle passivation portion230 m and the upper passivation portion 230 u of this embodiment maycorrespond to different materials than the middle passivation portion230 m and the upper passivation portion 230 u of FIG. 6. In thisembodiment, the concentration of Ge in the SiGeON layer may varyaccording to the concentration of Ge in the first silicon germaniumlayer 204 a and the second silicon germanium layer 204 b. For example,the upper passivation portion 220 u over the first silicon germaniumlayer 204 a may be expressed as Si_(x1)Ge_(y1)ON and the middlepassivation portion 220 u over the second silicon germanium layer 204 bmay be expressed as Si_(x2)Ge_(y2)ON.

FIG. 23 illustrates forming an STI oxide 212 in the trenches 210 (seeFIG. 22), creating recesses 214, in accordance with an embodiment.Similar processes as those disclosed above with reference to FIG. 7 maybe used. In an embodiment, a height H₃ of the fin 220 above an uppersurface of the STI oxide is about 20 nm to about 50 nm.

FIG. 24 illustrates a fin reshaping process and FIG. 25 illustrates asecond passivation process to form a second passivation layer 910 inaccordance with an embodiment. Similar processes as those disclosedabove with reference to FIGS. 8 and 9 may be used.

Thereafter, additional processes may be performed. For example, FIG. 26illustrates a gate structure 912 formed over portions of the fin 220.Similar processes and structures may be used as discussed above withreference to FIG. 10.

The embodiments discussed above may be selected for a particularapplication. For example, an embodiment utilizing a Ge fin may be bettersuited for an N-FET, whereas SiGe may be better suited for a P-FET.Particular embodiments may be selected to achieve the desired strain anddefect control. Furthermore, the percentage of Ge in SiGe may beadjusted to obtain the desired strain.

In an embodiment, a FinFET is provided. The FinFET comprises a substrateand a fin structure protruding from the substrate, the fin structurecomprising one or more semiconductor layers, each of the semiconductorlayers having a different lattice constant of a correspondingimmediately underlying layer. An isolation region is adjacent opposingsidewalls of the fin structure, the fin structure having an upperportion extending above the isolation region, the upper portion havingslanted sidewalls. A first passivation layer is interposed between thefin structure and the isolation region, and a second passivation layeris on the upper portion of the fin structure. A gate structure overliesthe upper portion of the fin structure. The fin structure may comprise,for example, a silicon germanium layer on a silicon substrate and agermanium layer on the silicon germanium layer. In other embodiments,the fin structure may comprise a silicon germanium layer on a siliconsubstrate. In in yet other embodiments, the fin structure may comprisemultiple silicon germanium layers having different germaniumconcentrations on a silicon substrate.

In yet other embodiments, a method of forming a FinFET is provided. Themethod includes providing a substrate and forming one or more finsextending from the substrate, each of the one or more fins having one ormore semiconductor layers overlying the substrate, each of the one ormore fins having a lattice constant different than a lattice constant ofan underlying layer. A first passivation layer is formed over the one ormore fins, and isolation regions are formed along opposing sidewalls ofthe one or more fins such that the one or more fins extending above anuppermost surface of the isolation regions. A reshaping process isperformed on exposed portions of the one or more fins, and a secondpassivation layer is formed over the reshaped exposed portions of theone or more fins.

In yet still other embodiments, a FinFET is provided. The FinFETincludes a substrate, a fin structure protruding from the substrate, thefin structure comprising one or more semiconductor layers, each of thesemiconductor layers having a different lattice constant of animmediately underlying layer, and an isolation region adjacent opposingsidewalls of the fin structure, the fin structure having an upperportion extending above the isolation region, the upper portion havingslanted sidewalls. The FinFET further includes a first passivation layerinterposed between the fin structure and the isolation region and asecond passivation layer on the upper portion of the fin structure. Agate structure overlies the upper portion of the fin structure.

In yet still other embodiments, a FinFET is provided. The FinFETincludes a substrate having a fin structure, the fin structurecomprising one or more semiconductor layers, each of the semiconductorlayers having a different lattice constant of an immediately underlyinglayer, the fin structure having a lower portion and an upper portion,the upper portion having a lesser slope than the lower portion and anisolation region adjacent opposing sidewalls of the fin structure, anupper surface of the isolation region being level with a junctionbetween the upper portion and the lower portion. The FinFET furtherincludes a first passivation layer interposed between the fin structureand the isolation region and a second passivation layer on the upperportion of the fin structure. A gate structure overlies the upperportion of the fin structure.

In yet still other embodiments, a FinFET is provided. The FinFETincludes a fin structure comprising one or more semiconductor layers,each overlying semiconductor layer of the one or more semiconductorlayers having a different lattice constant of a correspondingimmediately underlying semiconductor layer of the one or moresemiconductor layers, the fin structure having a lower portion and anupper portion. The FinFET further includes a first passivation layeralong sidewalls of the lower portion of the fin structure, an isolationregion over the first passivation layer along opposing sidewalls of thefin structure, and a second passivation layer on sidewalls of the upperportion of the fin structure, an interface between the first passivationlayer and the second passivation layer being aligned with an uppersurface of the isolation region. A gate dielectric layer overlies thesecond passivation layer, and a gate electrode overlies the gatedielectric layer.

While the disclosure has been described by way of example and in termsof the preferred embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A method of forming a fin field effect transistor(FinFET), the method comprising: forming a first fin extending from asubstrate, the first fin having one or more semiconductor layersoverlying the substrate, each of the one or more semiconductor layershaving a lattice constant different than a lattice constant of anunderlying layer, wherein an uppermost semiconductor layer of the one ormore semiconductor layers comprises a germanium-containing semiconductormaterial; forming a first passivation layer over the first fin, whereinthe first passivation layer over the uppermost semiconductor layercomprises an oxynitride of the germanium-containing semiconductormaterial; after forming the first passivation layer, forming isolationregions along opposing sidewalls of the first fin; removing the firstpassivation layer above an upper surface of the isolation regions, thefirst fin extending above an uppermost surface of the isolation regionsand an upper surface of the first passivation layer; etching portions ofthe first fin extending above the upper surface of the isolation regionsto form a reshaped portion of the first fin, wherein after etching,sidewalls of the first fin above the first passivation layer has adifferent slope than sidewalls of the first fin adjacent the firstpassivation layer; forming a second passivation layer over the reshapedportion of the first fin, wherein the second passivation layer over thereshaped portion of the first fin comprises an oxynitride of thegermanium-containing semiconductor material; and forming a gatestructure over the second passivation layer.
 2. The method of claim 1,wherein the germanium-containing semiconductor material is germaniumlayer.
 3. The method of claim 2, wherein the germanium layer is on asilicon germanium layer.
 4. The method of claim 2, wherein the secondpassivation layer is germanium oxynitride.
 5. The method of claim 4,wherein the germanium oxynitride is GeO_(x)N_(y), having a ratio of y:x(N:O) in a range from 0.25 to 0.9.
 6. The method of claim 1, wherein thegate structure comprises a gate dielectric.
 7. The method of claim 1,wherein a width of the first fin at a bottom of the second passivationlayer is in a range from 6 nm to 20 nm.
 8. A method of forming a finfield effect transistor (FinFET), the method comprising: forming a firstpassivation layer over a fin on a substrate, wherein the fin comprises aplurality of semiconductor layers having different lattice structures,wherein the plurality of semiconductor layers comprises a firstsemiconductor layer, wherein the first semiconductor layer comprises agermanium-containing semiconductor material, wherein the firstpassivation layer comprises an oxynitride of the germanium-containingsemiconductor material; after forming the first passivation layer,forming an isolation region along a sidewall of the fin, an upperportion of the fin extending above an upper surface of the isolationregion, wherein the upper portion comprises the first semiconductorlayer; after forming the isolation region, reshaping the upper portionof the fin to form a reshaped portion of the fin, wherein afterreshaping a sidewall of the upper portion of the fin extends away fromthe upper surface of the isolation region at a different angle than asidewall of a lower portion of the fin extends away from the uppersurface of the isolation region; forming a second passivation layer overthe reshaped portion of the fin, wherein the second passivation layercomprises an oxynitride of the germanium-containing semiconductormaterial; and forming a gate structure over the reshaped portion of thefin.
 9. The method of claim 8, wherein the second passivation layer hasa thickness in a range from 0.5 nm to 5 nm.
 10. The method of claim 8,wherein the second passivation layer comprises GeO_(x)N_(y).
 11. Themethod of claim 8, wherein the second passivation layer has a firstratio of y:x along a top surface of the fin and a second ratio of y:xalong a sidewall of the fin, wherein the first ratio is different thanthe second ratio.
 12. The method of claim 11, wherein the first ratio isgreater than the second ratio.
 13. The method of claim 11, wherein aratio of the first ratio to the second ratio is in a range from 1 to1.3.
 14. The method of claim 12, wherein forming the second passivationlayer comprises a plasma process.
 15. A method of forming a fin fieldeffect transistor (FinFET), the method comprising: forming a fin over asubstrate, the fin having at least one semiconductor layer having adifferent lattice constant than a lattice constant of the substrate,wherein the at least one semiconductor layer comprises an upper layercomprising a germanium-containing semiconductor material; forming afirst passivation layer over the fin, wherein the first passivationlayer over the at least one semiconductor layer comprises an oxynitrideof the germanium-containing semiconductor material; after forming thefirst passivation layer, forming isolation regions along opposingsidewalls of the fin, an exposed portion of the fin being free of theisolation regions; performing an etch process on the exposed portion ofthe fin to form a reshaped upper portion of the fin, wherein sidewallsof the reshaped upper portion of the fin are tapered such that a widthof the reshaped upper portion of the fin decreases as the fin extendsaway from the isolation regions; and forming a gate structure over thereshaped upper portion of the fin.
 16. The method of claim 15, furthercomprising forming a second passivation layer on the reshaped upperportion of the fin, the second passivation layer being an oxynitridehaving a different ratio of nitrogen to oxygen on an upper surface ofthe reshaped upper portion of the fin than along a sidewall of thereshaped upper portion of the fin.
 17. The method of claim 16, whereinforming the gate structure comprises forming a gate dielectric layerdirectly on the second passivation layer.
 18. The method of claim 16,wherein the second passivation layer is a germanium oxynitride layer,wherein the germanium oxynitride layer directly contacts a silicongermanium oxynitride passivation layer along a lower portion of the fin.19. The method of claim 15, wherein forming the fin comprises formingthe upper layer directly on a silicon germanium layer.
 20. The method ofclaim 15, wherein performing the etch process removes the firstpassivation layer above an upper surface of the isolation regions.